LaTeX Templates New Box 4

\documentclass[12pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath,amssymb,amsfonts,tikz}
\usepackage[left=3.3cm,right=1cm,top=1.5cm,bottom=2.5cm]{geometry}
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\everymath{\displaystyle}
\usetikzlibrary{shadows}
\pagestyle{empty}
\usepackage{pifont,fourier}
\usetikzlibrary{shapes.arrows,calc} 
\linespread{1.3} 
\usepackage{amsmath,amsfonts,amssymb,tikz,enumitem}
%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{eso-pic}
\AddToShipoutPictureBG{
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\node[scale=2,rotate=0] at([xshift=4cm,yshift=-3.3cm]current page.north west){\color{col1}{\large \textbf{\textit{Chapitre 3}}}};
\node[anchor=west,scale=4] at([xshift=-7cm,yshift=-6cm]current page.north){\color{col1!75!black}{ \textbf{\textit{ Nombres Complexes}}}};
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\node[anchor=west] at([xshift=4cm,yshift=-8.5cm]current page.north west){\color{col1}{\Large \textbf{{Résumé de cours}}}};
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%%%%%%%%%%%%%
\usepackage{tcolorbox}
\tcbuselibrary{skins,breakable}
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%%%%%%%%%%
\begin{document}
\ \vskip8cm
\begin{tcolorbox}
 \begin{minipage}{8cm}
 \begin{enumerate}[font=\sffamily\bfseries,label=\arabic*), series=Is]
 \item Si $z=x+iy$ avec $x$ et $y$ réels, alors\\
 $|z|=\sqrt{x^2+y^2}$.
 \item $z=0\Leftrightarrow |z|=0$
 \item $|zz'|=|z|\times |z'|$
 \item $\left|z^n\right|=|z|^n$ ($n\in\mathbb{N}^*$)
 \end{enumerate}
 \end{minipage}  \begin{minipage}{8cm}
 \begin{enumerate}[label=\arabic*),resume*=Is]
 \item $\left|\dfrac{1}{z}\right|=\dfrac{1}{|z|}$ ($z\neq 0$)
 \item Si $z'\neq 0$, $\left|\dfrac{z}{z'}\right|=\dfrac{|z|}{|z'|}$
 \item Inégalité triangulaire ; $|z+z'|\leqslant |z|+|z'|$ \\
 (mais on n'a pas égalité en général) \end{enumerate}
 \end{minipage}
\end{tcolorbox}
\end{document}